Photoelectron spectroscopic characterization of the niobium-benzene anion produced by reaction of niobium with ethylene

We report the 488 nm photoelectron spectrum of the NbC₆H₆^- anion produced by reaction with ethylene in a flow tube reactor equipped with a niobium cold cathode discharge source. The vibrationally resolved photoelectron spectrum of the mass-selected NbC₆H₆^- product is the same as that obtained upon reaction with benzene. Through comparison with the results of density functional calculations, the observed state of NbC₆H₆^- is assigned as the ³A₁ ground state of an η⁶ Nb-benzene complex. Photodetachment transitions access the ²A₁ ground state of neutral NbC₆H₆ and an excited state 0.713 ± 0.004 eV higher in energy, also assigned as a ²A₁ state. Vibrational frequencies for the totally symmetric modes active in each transition are reported for the protonated and perdeuterated complexes. The electron affinity of NbC₆H₆ is 0.893 ± 0.006 eV.